where do cells come from?
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Where Do Cells Come From?. “ All cells come from pre-existing cells ” -Cell Theory 3 types of cell divisions : Mitosis -nuclear cell division in somatic cells, asexual reproduction Meiosis -nuclear cell division in germ cells, sexual reproduction - PowerPoint PPT PresentationTRANSCRIPT
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Where Do Cells Come From?“All cells come from pre-
existing cells” -Cell Theory
3 types of cell divisions:
Mitosis-nuclear cell division in somatic cells, asexual reproduction
Meiosis-nuclear cell division in germ cells, sexual reproduction
Prokaryotic Fission-cell division in bacteria cells, asexual reproduction
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Review of Terms used in Mitosis/Meiosis Somatic cells-all cells except
sex cells Germ cells-sex cells, sperm
and eggs Diploid-2 of every
chromosome Haploid-1 of each
chromosome Chromosome-a linear
arrangement of genes, composed of DNA
How many chromosomes are found in humans?
Which cells are diploid and haploid in humans?
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Review of Terms used in Mitosis/Meiosis Chromatid-1 arm of
duplicated chromosome, sister chromatids
Centromere-area on chromosome that holds chromatids together
Histones-proteins associated with chromosomes, organize structure
Nucleosome-1 unit of DNA + 8 histones
Chromatin-all DNA + histones + other proteins
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Eukaryotic Cell CycleInterphase-3 phasesG1-initial growth, G0 resting phase, permanently
arrestedS-synthesis, DNA is duplicatedG2-final preparations before mitosis, microtubule
formationMitosis-4 phases: Prophase, Metaphase, Anaphase,
TelophaseCytokinesis-division of cytoplasm
Most adult cells are in what phase of the cell cycle?
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Control of the Cell Cycle Tightly regulated, require signals Cyclins required for cells to move
from G1S, G2M In mammalian cells p53 stops cycle
if DNA is damaged, hasn’t finished replicating, or if chromosomes are not attached to spindle
High levels result in apoptosis programmed cell death through caspases
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MitosisProduces 2 identical diploid daughter cells
from 1 parent cellHave the same DNA clonesUsed for growth and repairAsexual reproduction used by some members
of fungi, plants, animals, protists
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Mitosis-PMATProphaseChromosomes
condenseNucleolus
disappears, nuclear envelope breaks apart
Centrioles duplicate, move to opposite poles
Microtubules grab chromosomes in order to move them
Longest phase
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Mitosis-PMATMetaphase-
microtubules align chromosomes at the equator of a cell, “metaphase plate”
Kinetochore spindle fibers attached to sister chromatids come from poles
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Mitosis-PMATAnaphase-pulling apart
of chromatids/centromeres, microtubules contract, moving chromatids to opposite poles, “spindle apparatus” is clearly visible
Shortest phaseTelophase-chromosomes
decondense, nuclear envelope reforms, nucleolus reappears
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Cytokinesis Division of cytoplasm Occurring
simultaneously with telophase
Occurs differently in plant and animal cells
Cell plate formation-Plant cells
Vesicles from golgi align at equator and fuse to form cell wall
Cleavage Furrowing-Animal Cells
Actin filaments align at equator (contratile ring)and contract until separate cell into two
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Stem Cells and CloningStem cells adult cells that retain ability to divideCan differentiate into different types of cellsTherapeutic cloning produces human tissuesReproductive cloning new individual can be made
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Cloning and Embryonic Stem CellsEmbryonic Stem Cells (ES)-cells from an early
embryo; these cells have not received the genetic instructions to become a specialized cell yet
These cells can be transferred into a organ and become that type of tissue. Example: ES cells defective pancreas, become pancreas cells and start producing insulin
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Stem Cell Lines100s have already been created that are
heart, liver, pancreas, etc. cell linesEventually, transplant into humans; mice
studies are very promisingProblems: immune reaction Getting the cells to defective tissueEthical issues (no fertilized egg required)
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Properties of Cancer Cells: loss of cell cycle control(When Compared to Normal Cells)
Additional chromosomes, genes
Grow and divide abnormally (faster)
Less adhesive, don’t stick to each other
Metastasize-migrate to other locations
Don’t communicate with each other
Don’t apoptose (die)
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CancerUnregulated and
uncontrolled cellular growth
Form tumorsMetastasize
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Cancer: Loss of Genetic Controls over Cells
Cell growth and repair is tightly regulated by genes; when these genes fail Cancer
Proto-oncogene (accelerator) normal growth gene becomes mutated oncogene, BRCA1
Tumor suppressor genes (brakes) -control cell death, ex. p53 gene
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Causes of CancerUV, X-ray, gamma
radiation, chemicals in work places, smoking
Viruses Hepatitis C, liver cancer, HPV genital warts cervical cancer
Chromosome translocation leukemia
Carcinogens-cancer causing agents, ex. Compounds found in cigarettes
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Cancer : Tumors and Treatment Benign-slow growth, no metastasis,
not lethal unless size becomes largeMalignant-rapid growth, metastasize,
destroy tissue around themTreatmentChemotherapy-targets quickly
dividing cells, both cancer and healthyRadiation Therapy-high energy
radiation targets only tumor
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Prokaryotic Cell DivisionBinary fissionAsexual
reproductionNo nucleus, only
nucleoid regionSingle circular
chromosomeCell wall
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